1. Field of the Invention
The present invention relates to electrostatographic development apparatus, and more particularly to such a development apparatus including a magnetic development brush that has an extended development nip.
2. Description Relative to the Prior Art
Development apparatus are well known for use in an electrostatographic reproduction apparatus, such as in a copier or printer, for developing latent images which are formed electrostatically on an image-bearing surface. Such development apparatus include those having magnetic development brushes as disclosed, for example, in Japanese Patent No. Sho 55 (1980)-39406; U.S. Pat. Nos. 4,235,549 issued to Eisbein et al., 4,287,850 issued to Yamamoto et al.; and 4,928,145 issued to Okamoto et al.
As disclosed in each of the above patents, a magnetic development brush of such a development apparatus consists of a generally cylindrical magnetic core and a generally cylindrical non-magnetic shell surrounding such core. When the development apparatus is mounted for operation in a copier or printer, for example, the non-magnetic shell of the magnetic brush is located spaced from, and forms a development nip or footprint with the image-bearing surface in such a copier or printer. The magnetic core of the magnetic brush functions to attract magnetic developer material contained within the development apparatus onto the surface of the non-magnetic shell thereof thereby forming a magnetic developer material nap on such shell. Rotation of the magnetic core then causes such an attracted developer material nap to move or be transported over the surface of the shell, into and through the development nip where such nap contacts and develops electrostatic latent images on the image-bearing surface.
The quality of the images so developed depends in significant part, for example, (a) on the nature and height or thickness of the developer material nap being transported as above through the development nip; and (b) on the length of development time, that is, the time during which the latent images on the image-bearing surface are in actual contact with such a developer material nap. At any given development apparatus speed, such development time is determined of course by the size of the nip width or footprint of the development nip. As disclosed for example in the '549 patent to Eisbein and in the '850 patent to Yamamoto, the development quality of such images can be improved in part by providing means for increasing the width of the development nip, in other words, means for increasing the size of the nip width or footprint of the development nip.
Unfortunately, however, such an improvement alone does not ensure the consistency and desired thickness of the developer material nap, and alone can very easily be counteracted by an increase in the throughput speed of the development apparatus. Accordingly, there is still a need to provide means for significantly increasing the size of the nip width or footprint of a magnetic development brush while also still substantially providing a consistent and desirably thick developer material nap for transportation through such an extended development nip.